Coolant Temperature Sensor/Switch (For Computer): Description and Operation

ENGINE COOLANT TEMPERATURE SENSOR

The Engine Coolant Temperature Sensor (ECT) is a resistor based sensor. As coolant temperature increases, sensor resistance decreases. The ECM uses this information for hot and cold start strategies that require additional fuel delivery. It also uses this information to help determine when to enter closed loop operation.

A diagnostic trouble code is stored when the signal is out of range. The MIL will illuminate and the ECM will substitute a default value of 36°C (97°F).

Variations in engine operating temperature require variations in ignition timing to maintain the optimum balance between driveability and emissions. The ECM advances ignition timing when the engine is cold and retards it as the engine warms up. The coolant temperature sensor provides the ECM with data on which to base these timing decisions.